1. Field of the Invention
This invention relates a vapor-phase growing unit and a method of forming a vapor-phase-growth film, for forming the vapor-phase-growth film on a surface of a tabular or planar substrate such as, for example, a semiconductor wafer by using a plurality of source gases.
2. Description of the Related Art
Various processes are performed on a substrate made of, for example, a semiconductor wafer or the like, in a fabrication of a semiconductor device. For example, a plurality of source gases may be used in a method of forming a vapor-phase-growth film such as, for example, a CVD method and the like.
Particularly, it is possible to form a vapor-phase-growth film of SrTiO3 on a surface of a silicon wafer by a CVD method, in which, for example, an organic-metal including gas that includes strontium (Sr) and titanium (Ti) and oxygen gas are used. This vapor-phase-growth film is useful for example as a capacitor insulating film because of properties thereof.
Generally, formation of a vapor-phase growth film on a wafer by a plurality of source gases is performed usually by using a reaction container in which a plurality of gas-introducing tubes are arranged, placing the wafer in this reaction container, and heating while spouting the source gases form the respective gas-introducing tubes.
Usually, as for a gas-introducing tube in a conventional vapor-phase growing unit, a straight quartz tube having a gas-spouting port formed by a circular through hole at a peripheral wall thereof has been widely known. In addition, another tube having a gas-spouting port formed by a slit-like through hole extending along a circumferential direction thereof has also been known.
In the conventional vapor-phase growing unit, when an organic-metal including gas is used as a source gas, a front-face direction of the gas-spouting port of the gas-introducing tube is set to be oriented toward a center of a wafer so that the source gas is spouted in a direction toward the center of the wafer along a surface of the wafer. Nonetheless, practically, an in-plane ununiformity (ununiformity within the surface) in a vapor-phase-growth film formed on the surface of the wafer is significantly great. After all, there is a problem that it is impossible to form a vapor-phase-growth film having a high uniformity and desired properties.
For example, when an organic-metal including gas that includes strontium (Sr) and Titanium (Ti) and oxygen gas are used, a desired crystal growth cannot be generated on a substrate with a high in-plane uniformity, whereby it is impossible to form the objective vapor-phase-growth film.
Intensive studies on the above problem suggest that it is caused by a significantly great in-plane ununiformity in distribution of the organic-metal including gas on the surface of the wafer.
Specifically, the organic-metal including gas is a gas of high density. Accordingly, when the gas-spouting port of the gas-introducing tube has a circular shape, as for the formed vapor-phase-growth film, a certain degree of the uniformity can be obtained in a small area in a front-face direction of the gas-spouting port (that is to be a direction of a diameter R of the wafer). However, in a lateral direction vertical to the front-face direction, in proportion to the distance from the gas-spouting port, the film thickness is sharply decreased. That is, the state comes to a state of a great ununiformity.
Consequently, a gas-introducing tube whose gas-spouting port is formed by a slit-like through hole extending in a surface-direction of a wafer was used. As a result, the gas spreads in the lateral direction in an area of a small distance from the gas-spouting port. Therefore, as for the formed vapor-phase-growth film, the uniformity of the film thickness was improved in a certain degree in the lateral direction vertical to the front-face direction of the spouting port (that is to be the direction of a diameter R of the wafer). However, in the front-face direction, in proportion to the distance from the gas-spouting port, the film thickness is sharply decreased. After all, it reveals that the state becomes a state of a great ununiformity.